1. Field of the Invention
This invention relates to a sheet conveying apparatus applicable to an image forming apparatus such as a copying apparatus or an LBP and a sheet reading apparatus and an image forming apparatus provided with the sheet conveying apparatus. It particularly relates to a sheet conveying apparatus provided with a separating device and a sheet supplying device for separating and supplying out a plurality of sheets one by one, and mounting or conveying them on or to a predetermined position.
2. Related Background Art
A sheet conveying apparatus separates a plurality of sheets stacked on a tray or the like one by one in a sperating portion and supplies them to a predetermined position. Such a sheet conveying apparatus is applied to an automatic original feeding apparatus or the like for automatically feeding sheet-like originals to the image reading portion of an image forming apparatus such as a copying apparatus.
An example of an original conveying apparatus (sheet conveying apparatus) will hereinafter be described with reference to FIG. 49 of the accompanying drawings.
An original conveying apparatus 802 provided in an image forming apparatus 801 feeds a plurality of sheet-like originals stacked on an original tray 804 to a separating portion in succession from the uppermost sheet by the rotation of a sheet feeding roller 805. The separating portion is provided with a separating-conveying roller 808 rotatable in a sheet feeding direction, and a separating belt 806 rotatable in a direction for returning the originals, so that originals fed are separated and supplied one by one by the action of the separating-conveying roller 808 and the separating belt 806.
A first sheet supplying roller 816 supplies the originals separated and fed in this manner toward the downstream side, and abut them against a stationary second sheet supplying roller 809 to form a loop to thereby correct the skew-feed of the originals and to register the leading ends thereof with the second sheet supplying roller. Thereafter, at suitable timing, the second sheet supplying roller 809 is rotated to thereby further feed out the originals toward the downstream side. At this time, a drive roller 836 over which a conveying belt 807 is wound is rotatively driven, so that the original is conveyed on a platen 803 by the conveying belt 807 and is placed on a predetermined reading position.
As an image reading system, there is a system for reading an image while conveying an original with an image reading portion fixed (a flow-reading system), besides a system for reading an image while moving an image reading portion with an original fixed on the platen 803 (a fixed-reading system). These two systems are selectively used depending on the difference in the kind of sheet or the mode.
When the reading of the original image is finished, the conveying belt 807 is driven again to thereby convey the original to a sheet discharge tray 810. Finally, the original is discharged onto the sheet discharge tray 810 by sheet discharge rollers 811 and 812. In FIG. 49, the reference numeral 200 designates a reader unit for reading an image, and the reference numeral 300 denotes an image forming unit for forming an image.
In the above-described example of the prior art, however, when the originals are being separated and conveyed by the separating portion, the separating belt 806 is being rotated in a direction to return the original in order to binder the entry of the next original. Therefore, in some cases, the rectilinearity of conveyance of the original has been unstable.
Also, depending on the friction state of the surface of the original, the separating belt has come not to follow the rotation of the separating-conveying roller 808 (the slip of the original and the roller) and the separating-feeding time has sometimes been late. In such an apparatus, the presence of the occurrence of the delay in the separation of the original is monitored on the basis of the result of the detection by a separation sensor which monitors the originals. Therefore, in the worst case, it has been judged by a control device that a delay in the separation of the original has occurred (the sensor does not detect even when a predetermined time has passed), and the apparatus might been stopped.
Also, in the flow-reading mode, it is necessary during the reading of an image to separate the next original and convey it to a reading standby position. However, if a delay in separation occurs, the next original is not conveyed to the standby position, and therefore the time (productivity) for continuously reading the images of a plurality of originals is reduced. To prevent the occurrence of a delay in separation, it is conceivable to increase the separating-conveying speed. However, this may cause the leading end of the next original to abut against the trailing end of an original under the image reading to thereby cause sheet jam.